Messages in this thread |  | | Date | Fri, 7 Sep 2001 16:13:23 +0200 | From | antirez <> | Subject | Re: epic100.c, gcc-2.95.2 compiler bug! |
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On Fri, Sep 07, 2001 at 04:03:15PM +0200, Ingo Rohloff wrote: > BEWARE: DON'T USE gcc-2.95.2! > I compiled the linux-2.4.9 version with gcc-2.95.2. > And I can _definitely_ confirm that epic100.c triggers a compiler > bug. (I have the erronous assembler code on my harddisk if anyone is > interested.)
The following seems a gcc 3.0 bug, not sure it was fixed in gcc 3.01.
See the assembly generated with -O3 for the following code:
-------------------------------------------------------------- inline static long QInt(double inval) { long *l; char *c = (char*) &inval; inval = 68719476991.99;
l = (long*) (c+2); return *l; }
int main(void) { printf("%lu\n", QInt(OFFENDING_VALUE)); return 0; } ---------------------------------------------------------------
the above function is compiled as:
.file "test2.c" .section .rodata .LC0: .string "%lu\n" .text .align 16 .globl main .type main,@function main: pushl %ebp movl %esp, %ebp subl $48, %esp * movl $16776561, -32(%ebp) * movl -30(%ebp), %eax * movl $1110441984, -28(%ebp) pushl %eax pushl $.LC0 call printf addl $16, %esp movl %ebp, %esp xorl %eax, %eax popl %ebp ret .Lfe1: .size main,.Lfe1-main .ident "GCC: (GNU) 3.0"
Note the line I marked with "*". The double var is 8 byte, it is loaded moving two 32 bit words in the -32 and -28 offset. Unfortunatelly with -O3 the "*l" value get computed between the two 'movl', and not after the second movl.
This code is really unsane anyway but this seems a clear gcc 3.0 bug.
I hope that the gcc folks here may report the problem if not already known.
I didn't tested it but maybe the same problem exists with other 8 byte types like 'long long'.
regards, antirez - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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